THE ROLE OF INTRACELLULAR NA-INDUCED INTRACELLULAR FREE CA2+ CHANGES IN RAT FOREBRAIN NEURONS( AND MITOCHONDRIA IN BUFFERING OF KAINATE)

1. We have examined the mechanisms by which cultured central neurones from embryonic rat brain buffer intracellular Ca2+ loads following kai nate receptor activation using fluorescent indicators of [Ca2+](i) and [Na+](i). 2. Stimulation of cultured forebrain neurones with 100 mu M kainate produced a rapid increase in [Ca2+](i) that displayed a varia ble rate of recovery. Kainate also increased [Na+](i) with a response that was slightly slower in onset and markedly slower in recovery. 3. The recovery of [Ca2+](i) to baseline was not very sensitive to the [N a+](i). The magnitude of the increase in [Na+](i) in response to kaina te did not correlate well with the [Ca2+](i) recovery time, and experi mental manipulations that altered [Na+](i) did not have a large impact on the rate of recovery of [Ca2+](i). 4. The recovery of [Ca2+](i) to baseline was accelerated by the mitochondrial Na+-Ca2+ exchange inhib itor CGP-37157, suggesting that the recovery rate is influenced by rel ease of Ca2+ from a mitochondrial pool and also that variation in the recovery rate is related to the extent of mitochondrial Ca2+ loading. Kainate did not alter the mitochondrial membrane potential. 5. These s tudies reveal that mitochondria have a central role in buffering neuro nal [Ca2+]i changes mediated by non-N-methyl-D-aspartate (NMDA) glutam ate receptors, and that the variation in recovery times following kain ate receptor activation reflects a variable degree of mitochondrial Ca 2+ loading. However, unlike NMDA receptor-mediated Ca2+ loads, kainate receptor activation has minimal effects on mitochondrial function.